1. Field of the Invention
Embodiments described herein relate to thermal processing of semiconductor substrates. More specifically, embodiments described herein relate to methods and apparatus for laser thermal annealing of semiconductor substrates.
2. Description of the Related Art
Laser thermal processing is a commonly used technique in the semiconductor industry. Semiconductor substrates are subjected to laser thermal treatment for various recrystallization, activation, and annealing processes related to integrated circuits, large area panels such as flat-panel displays and solar panels, photonic media, and magnetic media. Laser processing is frequently selected for large heating rates achievable with laser means, and the rapid throughput available.
In most instances, a substrate to be processed is positioned on a support in a laser apparatus, and the laser is focused to a spot on the substrate. The substrate is then moved to position the laser spot at successive locations on the substrate until all desired locations on the substrate are processed. Positioning is normally accomplished using a precision x-y stage for supporting the substrate. The substrate may also be moved in a z-direction to maintain focus of the laser spot on the substrate.
As the size of devices on semiconductor substrates declines with Moore's Law, the need for accurate control of positioning and focus increases. Imprecision in positioning the laser may result in devices desirous of thermal processing being missed, while other locations not desirous of thermal processing are irradiated. In addition, uniform treatment becomes increasingly difficult as imprecision in focus of the radiation becomes larger relative to device size. These trends rapidly increase the difficulty of accurately positioning the stage in the x, y, and z-directions. Thus, there is a continuing need for thermal processing apparatus and methods that yield improved precision of location and focus.